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View Full Version : .223 vs 5.56 and .308 vs 7.62 ?????


Kauf
02-16-2012, 8:45 PM
When I did a conversion from .223 inches ---> mm I get .223in=5.66mm and when I convert .308--->mm I get 7.82 mm. Why then can some AR-15's shoot both 5.56mm and 5.66mm (equal to .223 in mm) and why do they say .308 rounds are the same as 7.62 NATO rounds? Thanks for clarifying!

Merc1138
02-16-2012, 8:53 PM
who says .308 is the same as 7.62 NATO? It isn't.

You can shoot .223 out of a 5.56 gun.

You can shoot 7.62 out of a .308 gun.

You shouldn't shoot 5.56 out of a .223 gun.

You shouldn't shoot .308 out of a 7.62 NATO gun.

There are different groups that set standards differently, and some of them happen to be close enough to be interchangeable in some circumstances.

By the way, the diameter of a .223 and 5.56 bullet is .224"(5.7mm).

NYY
02-16-2012, 8:57 PM
.223/5.56

http://www.ar15armory.com/forums/223-556-t25710.html

7.62x51/.308

http://forum.pafoa.org/general-2/45798-308-vs-7-62x51.html

Kauf
02-16-2012, 9:08 PM
who says .308 is the same as 7.62 NATO? It isn't.

You can shoot .223 out of a 5.56 gun.

You can shoot 7.62 out of a .308 gun.

You shouldn't shoot 5.56 out of a .223 gun.

You shouldn't shoot .308 out of a 7.62 NATO gun.

There are different groups that set standards differently, and some of them happen to be close enough to be interchangeable in some circumstances.

By the way, the diameter of a .223 and 5.56 bullet is .224"(5.7mm).

Why not just call them what they are instead of close to what they are? Very confusing...:facepalm:

Merc1138
02-16-2012, 9:18 PM
Why not just call them what they are instead of close to what they are? Very confusing...:facepalm:

Because bore diameter isn't the same as bullet diameter. You can also have multiple rounds with the same bullet diameter but everything else about the cartridge is completely different. Then there is a matter of organizations that I mentioned previously such as SAAMI.

robert101
02-17-2012, 9:08 AM
I shoot a lot of 308 out of a 7.62x51 barrel. No problem. Ever see metric dies? My dies are labeled 308 and I use them on NATO brass all the time.

chicoredneck
02-17-2012, 9:14 AM
Your using two different numbers. Bore vs bullet diameter.

1859sharps
02-17-2012, 10:03 AM
here is what fulton armory has to say about 308 vs 7.62

http://www.fulton-armory.com/%5Cfaqs%5CM14-FAQs%5C308.htm

here is what they say about 223 vs 556...little bit of self promotion in this explanation, but it does a decent job of explaining the chamber difference.

http://www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5C556-vs-223-Chambers.htm

308 vs 7.62...It is my understanding the difference in the real world, with a few exceptions is mostly a technical on paper difference and one most people won't ever encounter.

on the 223 verse 556. this one you do need to have your head wrapped around as more people are at risk of running into it. It's been a while since I "geeked" out on rifle specs, but where you are most likely to run into the difference is bolt action rifles and guns of non military heritage, such as the Mini 14 should NOT be used with mil spec 556 rounds.

I believe, but don't quote me without checking, that some and possibly all current mini 14s now come with 556 chambers. I seem to remember reading that somewhere. But again, don't take my word simply because I think I remember reading it. double check for your self.

In rifles of military heritage such as the ARs, I believe (but again it is up to you to do the due diligence) all main stream reputable manufactures are using 556 chambers these days. If you see 223 stamped on the barrel, question them on this. if they know what they are doing a barrel stamped with 223 should be different than a barrel stamped with 556. I believe the final say legally is what is on the barrel, not what is on the receiver.

1859sharps
02-17-2012, 10:05 AM
I shoot a lot of 308 out of a 7.62x51 barrel. No problem. Ever see metric dies? My dies are labeled 308 and I use them on NATO brass all the time.

It's not the actual bullet that is the issue here, its chamber specs and powder charges leading to differing chamber pressures that make up the differences in 223/556 and 308/7.62